D. c. voltage regulator with resistive restarting means



H. J. LUETTGE ET L D.C. VOLTAGE REGULATOR WITH RESISTIVE RESTARTING MEANS Filed March 11, 1966 INVENTORS HANS J. LUETTGE CHANDRA K. BAJPAI WWW ATTORNEYS.

United States Patent 3,384,808 D.C. VOLTAGE REGULATOR WITH RESISTIVE RESTARTING MEANS Hans J. Luettge and Chandra K. Bajpai, Ottawa, 0ntario, Canada, assignors to Northern Electric Company Limited, Montreal, Quebec, Canada Filed Mar. 11, 1966, Ser. No. 533,508 7 Claims. (Cl. 32322) The present invention relates to an improvement in transistorized direct-current voltage regulator circuits including a transistor whose emitter-collector internal circuit is connected in series with a source of unregulated D.C. voltage and a load. In particular this invention provides means effective to initiate conduction of the transistor upon energization of the regulator circuit by means of a source of unregulated D.C. voltage.

Direct-current voltage regulator circuits are well known in the art and provide low resistance D.C. voltage sources i.e. sources adapted to produce D.C. voltages which remain substantially constant over predetermined ranges of output current demands.

In general a transistorized direct-current voltage regulator circuit comprises an output sensing stage for producing an error signal responsive to deviation of the circuits output voltage from a predetermined value, a driver transistor for amplifying the error signal, and a series transistor whose emitter-collector internal circuit is connected between the input and output of the regulator circuit and whose conductivity is controlled by the amplified error signal.

A problem inherent to such circuits is one of starting since prior to connection of the input of the regulator circuit to a source of D.C. voltage the emitter-collector internal circuit of the series transistor presents an open circuit with the result that upon connection to a source of D.C. voltage the output voltage remains substantially zero and the output sensing stage is incapable of producing an error signal sufficient to drive the series transistor into conduction.

Various proposals have been made in the past to modify the circuits referred to in order to solve this problem. However, such modified regulator circuits displayed various objectionable characteristics. For instance it is known to shunt the emitter-collector internal circuit of the series transistor with a resistor so as to allow current to flow to the load and establish an output voltage sufficient to drive the output sensing stage. This solution however is not entirely satisfactory where good regulation is required since a shunt resistor having too high an ohmic value could not supply enough current to the load to drive the output sensing stage while a low resistance would adversely affect the circuits regulation. It is likewise possible to start the above-mentioned regulator circuit by means of a back-biased Zener diode in series with a resistor across the base-collector junction of the series transistor as described in the Reid et al. Canadian application Ser. No. 907,974 filed July 24, 1964 and assigned to the assignee of the present application. However, this modification in effect virtually cancels the circuits inherent short-circuit protection. This protection generally is very important in order to prevent excessive currents through the series transistor.

We have found that it is possible to overcome difficulties associated with prior regulator circuits of the type referred to above by providing electrical resistance means to establish a current flow path between the input terminals of the regulator circuit via the base-emitter junction of the series transistor.

It is therefore an object of the present invention to provide, in a transistorized direct-current voltage regulator 3,384,898 Patented May 21, 1968 "ice circuit of the type referred to, means capable of starting the circuit without incurring any appreciable reduction in regulation and which still allows short-circuit protection of the series transistor thereof.

Accordingly the present invention provides a D.C. voltage regulator circuit comprising: first and second input terminals for connection to a source of D.C. voltage; first and second output terminals for connection to a load; a series transistor having base, emitter and collector electrodes of which the emitter and collector electrodes are connected to the first input and output terminals respectively; a driver transistor having base, emitter and collector electrodes of which the emitter electrode is coupled to the base electrode of said series transistor and of which the collector electrode is connected to one of said output terminals; an output sensing stage connected to said output terminals for applying to the base electrode of said driver transistor an error current signal responsive to deviation of the voltage across said output terminals from a preselected value; and electrical resistance means connected between the base electrode of said driver transistor and said second input terminals for providing a minimum drive current to the base electrode of said series transistor to cause conduction thereof independently of said error current signal.

In the accompanying drawing, the single figure is a circuit diagram of a transistorized D.C. voltage regulator circuit in accordance with the present invention. The D.C. voltage regulator circuit illustrated generally comprises negative and positive input terminals represented by reference numerals 10, 11 and corresponding output terminals 12, 13, a series NPN transistor 14, an NPN driver transistor 15 and an output sensing stage 16.

The output sensing stage 16 comprises a bridge circuit 20 and a PNP pro-amplifier transistor 21. The bridge circuit 20 comprises two parallel arms connected across the output terminals 12 and 13. The first arm is potential divider formed by fixed resistors 22 and 24 and a potentiometer 23- having a movable arm or tap 25. The second arm comprises a Zener diode 26 having its anode connected to the negative output terminal 12 and its cathode connected at 27 to a resistor 28. In this arrangement the voltage at tap 25 is representative of the output voltage of the circuit whereas the voltage at 27 is substantially equal to the breakdown voltage of the back-biased Zener diode 26 provided that the voltage between the output terminals 12 and 13 exceeds the breakdown voltage of the Zener diode 26. Therefore bridge circuit 20 provides an error voltage signal (voltage between 27 and 25) which is responsive to deviation of the output voltage froma predetermined value. This value may be adjusted by means of potentiometer 23. The error voltage signal is applied to the base-emitter junction of pre-amplifier transistor 21 to control its collector current, which current is, in effect, an error current signal.

The error current signal from the output sensing stage 16 is applied to the base electrode of driver transistor 15 via a current limiting resistor 29. Driver transistor 15 amplifies the error current signal and applies it to the base (control) electrode of series transistor 14, thereby controlling the resistance of the emitter-collector internal circuit of series transistor 14.

The regulator circuit as thus far described is known in the prior art. It may have excellent regulation provided that the gain of the preamplifier and driver transistors 21 and 15 and the sensitivity of the output bridge 20 are suitably high. Moreover this circuit inherently provides high-current protection for its series transistor 14 in the event of short-circuit at the output terminals 12, 13. In fact, in the absence of output voltage, such as under shortcircuit condition, the voltage between junctions 27, 25 is zero and consequently the series transistor 14 appears substantially like an open circuit with the result that output current becomes substantially zero. As mentioned before, however, this feature although desirable presents a problem of starting.

This problem is overcome by the provision of an electrical resistance means such as resistor 30 between the base electrode of driver transistor 15 and the second input terminal 11. This resistance establishes a current flow path between the input terminals 10, 11 via the base electrode of series transistor 14. The ohmic value of resistor 30 should be such as to provide minimum drive current to the base electrode of the series transistor 14 to cause conduction thereof independently of any error current signal, for example a few megohms.

By using a sufficiently high resistance between the base of driver transistor 15 and the input terminal 11 the regulation of the circuit remains substantially unafiected and the collector current of the series transistor 14 under short-circuit condition is much too small to cause damage thereto.

As will be apparent to persons skilled in the art the circuit illustrated in the drawing would start equally well if the resistor 30 were connected between the base of series transistor 14 and the input terminal 11. However, the power handling capacity of such a resistor would need to be that of resistor 30 of the embodiment illustrated in the drawing multiplied by a factor corresponding to the current gain of the driver transistor 15.

While the embodiment hereinbefore described provides a regulated output of negative polarity (terminal 12), it will be obvious to those skilled in the art that this invention applies equally well to positive regulator circuits and transistors 14 and 15 may be of the PNP type provided that pro-amplifier transistor 21 is NPN.

In an actual circuit according to the invention and referring to the drawing the following components were used:

Transistors:

14 2N3442 15 2N699 21 2N1132 Resistors:

22 10,000 24 59,000 29 4,300 30 meg 3.9 Potentiometer 23 10,000 Zener diode 26 volt 6.2 Supply voltage at 10, 11 V. DC. (approx.) 35

The circuit using the above listed components had an output voltage of 28 DO. volts at 1 amp. load.

What we claim as our invention is:

1. A DC. voltage regulator circuit comprising:

(a) first and second input terminals for connection to a source of DC. voltage;

(b) first and second output terminals for connection to a load;

(c) a series transistor having base, emitter and collector electrodes of which the emitter and collector electrodes are connected to the first input and output terminals respectively;

(d) a driver transistor having base, emitter and collector electrodes of which the emitter electrode is coupled to the base electrode of said series transistor, and of which the collector electrode is connected to one of said output terminals;

(e) an output sensing stage connected to said output terminals for applying to the base electrode of said driver transistor an error current signal responsive to deviation of the voltage across said output terminals from a preselected value; and

(f) electrical resistance means connected between the base electrode of said driver transistor and said second input terminal for providing a minimum drive current to the base electrode of said series transistor to cause conduction thereof independently of said error current signal.

2. Apparatus as defined in claim 1 wherein said output sensing stage comprises a bridge circuit for producing a voltage signal responsive to deviation of the voltage across said output terminals from said preselected value, and means for transforming said voltage signal to said error current signal.

3. Apparatus as defined in claim 2 wherein said lastmentioned means includes a pre-amplifier transistor having a base-emitter junction and a collector electrode which is coupled to the base electrode of said driver transistor, said voltage signal being applied across the baseemitter junction of said pre-amplifier transistor, and the collector electrode of the pre-amplifier transistor supplying said error signal.

4. Apparatus as defined in claim 3, wherein the collector electrode of the driver transistor is connected to said first output terminal.

5. Apparatus as defined in claim 1 wherein said electrical resistance means is a resistor having a resistance of the order of a few megohms.

6. Apparatus as defined in claim 4 wherein said series and driver transistors are of the NPN type whereas said pre-amplifier transistor is PNP.

7. Apparatus as defined in claim 3 wherein said electrical resistance means is a resistor having a resistance of the order of a few megohrns.

References Cited UNITED STATES PATENTS 2,922,945 l/l960 Norris et 211. 3,204,175 8/1965 Kuriger. 3,319,150 5/1967 Elich et al. 3,344,340 9/1967 Webb.

JOHN F. COUCH, Primary Examiner. WARREN E. RAY, Examiner.

A. D. PELLINEN, Assistant Examiner. 

1. A D.C. VOLTAGE REGULATOR CIRCUIT COMPRISING: (A) FIRST AND SECOND INPUT TERMINALS FOR CONNECTION TO A SOURCE OF D.C. VOLTAGE; (B) FIRST AND SECOND OUTPUT TERMINALS FOR CONNECTION TO A LOAD; (C) A SERIES TRANSISTOR HAVING BASE, EMITTER AND COLLECTOR ELECTRODES OF WHICH THE EMITTER AND COLLECTOR ELECTRODES ARE CONNECTED TO THE FIRST INPUT AND OUTPUT TERMINALS RESPECTIVELY; (D) A DRIVER TRANSISTOR HAVING BASE, EMITTER AND COLLECTOR ELECTRODES OF WHICH THE EMITTER ELECTRODE IS COUPLED TO THE BASE ELECTRODE OF SAID SERIES TRANSISTOR, AND OF WHICH THE COLLECTOR ELECTRODE IS CONNECTED TO ONE OF SAID OUTPUT TERMINALS; 